1) Field of the Invention
The present invention relates to a low temperature sealing glass composition, and more particularly to a low temperature sealing glass composition suitable for hermetic sealing for ceramic packages, display devices, and the like.
2) Description of the Prior Art
Conventionally, various types of hermetic sealing materials for ceramic packages, display devces, and the like, such as a sealing material formed from a low melting glass powder, or such a glass powder mixed with a low thermal expansion, ceramic fillers to provide a sealing material with reduced expansion and increased strength, are conventionally known. PbO-B.sub.2 O.sub.3 based glass powder, and the PbO-B.sub.2 O.sub.3 based glass powder mixed with a low thermal expansion, ceramc fillers, are widely used at the present time as the sealing materials of the above-mentioned type. However, it is very difficult to prepare suoh a material with a sealing temperature of 400.degree. C. or less, therefore these sealing materials cannot be used with a ceramic package which must be sealed below 400.degree. C. when containing a heat sensitive element such as a highly integrated IC or a special crystal osclllator or the like.
Recently, because of this situation, efforts are being made to develop sealing materials with a sealing temperature of 400.degree. C. or less, centered around a sealng material made from a PbO-B.sub.2 O.sub.3 -Tl.sub.2 O based or a PbO-B.sub.2 O.sub.3 -F.sub.2 based glass powder, and these types of glass powders mixed with a low thermal expansion, ceramic fillers. The sealing temperature of each of these sealing materials is around 380.degree. C., but when using a sealing material made from the PbO-B.sub.2 O.sub.3 -Tl.sub.2 O based glass powder or the PbO-B.sub.2 O.sub.3 -Tl.sub.2 O based glass powder mixed with a low thermal expansion ceramic fillers, special equipment is necessary to prevent scattering of dust during the manufacturing or sealing operations because Tl.sub.2 O is a toxic substance. When a sealing material made from the PbO-B.sub.2 O.sub.3 -F.sub.2 based glass powder or the PbO-B.sub.2 O.sub.3 -F.sub.2 based glass powder mixed with low thermal expansion ceramic fillers is used, the electrical resistance deteriorates resulting in poor reliability. In addition, when this material is used to seal a display device such as CRT and Vacuum Fluorescent Display (VFD), the F.sub.2 gas released during sealing causes breakdown of the cathode material. Sealing materials made from a PbO-V.sub.2 O.sub.5 -Bi.sub.2 O.sub.3 based glass powder or the PbO-V.sub.2 O.sub.5 -Bi.sub.2 O.sub.3 based glass powder mixed with .degree. low thermal expansion ceramic fillers, as disclosed in U.S. Pat. No. 4,743,302, have a lower sealing temperature than the previously mentioned PbO-B.sub.2 O.sub.3 -Tl.sub.2 O based sealing materials and PbO-B.sub.2 O.sub.3 -F.sub.2 based sealing materials. Specifcally, sealing is possible at 370.degree. C. or lower. These sealing materials have extremely low sealing temperatures, but there is a strong tendency toward crystallization, so that on heating, crystallization occurs and the flowability becomes poor. Therefore these materials exhibit the drawback that unless a suitabe oad is applied during sealng, a desirable sealed member cannot be obtaned.